1. Technical Field
The embodiments herein generally relate to wireless communication systems, and, more particularly, to mobile television (TV) multicast technology.
2. Description of the Related Art
The MediaFLO™ (Forward Link Only) mobile multimedia multicast system available from Qualcomm, Inc., California, USA, is an alternative mobile multicast technology for the efficient transmission of multimedia data streams to mobile devices using TV. Multimedia streams can comprise various channels coming from different sources. The smallest channel transmission unit is called a Multicast Logical Channel (MLC). Each MLC is composed of three streams plus parity bits for error detection as indicated in FIG. 1. These streams are multiplexed/demultiplexed to/from a single MLC in a layer called the stream layer.
Streams 1 and 2 carry audio and video information of the channel requested by the user, while stream 0 carries control information used in the decryption of these audio and video information at the receiver, a number of MLCs are multiplexed together in the time domain to form a frame, and then four frames are packed together in addition to overhead information to form a super-frame having a duration of one second.
A super-frame is divided into four portions as shown in FIG. 2: Time-Division Multiplexing (TDM) pilots, Overhead Information Symbols (OIS), Data, and Pilot Positioning Channel (PPC). TDM1 is the first symbol of a super-frame and marks its beginning. In addition to being used for frame synchronization, TDM1 can also be used for initial time and frequency synchronization, so the receiver can immediately start decoding the information carried by the OIS. The OIS contain the time-frequency allocation for each MLC in the current super-frame. With respect to data, when an MLC is transmitted in a super-frame the payload is divided into four equal bursts, with each burst transmitted in a unique frame. The PPC can be used for transmitter identification and/or position location at the receiver. Super-frames are transmitted in sequence to be received at the service user. To ensure correct reception there must be synchronization between the transmitter and the receiver, and then several steps are performed to get the data streams ready for display.
The scenario at the receiver is as follows. First, the receiver looks for the TDM1 symbol which indicates the beginning of a super-frame as shown in FIG. 3(A). Then, the receiver looks for the OIS symbols to get all the information about the specific location of the MLC in the current super-frame that belongs to the channel required by the user. Second, as the receiver reaches the MLC in any of the four frames, it starts looking for stream 0 to extract several messages (Entitlement Control Messages (ECM) and Encryption Information Messages (EIM)).
Third, the receiver uses these messages, in addition to a message related to each user (Entitlement Management Message (EMM)) defined by the service provider, to be able to extract the code word (CW), which is the key used in the descrambling process as shown in FIG. 3(B). Finally, the receiver uses that CW to descramble the audio and video information contained in streams 1 and 2. This scenario is repeated every super-frame to guarantee efficient reception of data. However, there are some problems associated with this process. One example is shown in FIG. 3(A). First, as previously mentioned, there are several steps performed at the receiver before audio and video data of the required channel are ready to be displayed to the user. Moreover, streams of data are transmitted serially and the third step at the receiver requires getting stream 0, which is found at the end of an MLC after stream 1 and 2. This means that data are at the receiver, but not yet ready for the user as stream 0, needed for CW extraction for descrambling process, comes after data i.e. there must be a buffering stage for the streams queued at the receiver until the CW is ready for the descrambling process.
Second, these steps take approximately 0.5 to 0.75 sec. which is ½ to ¾ of a super-frame (1 sec.). This means that the delay introduced when the user turns on the channel is very large and also during switching from one channel to another; i.e., long channel switching delay. Accordingly, there remains a need to enhance the stream layer transmission for the MediaFLO™ mobile multimedia multicast system.